strata and shield volcanoes

Strata volcano

 Stratovolcanoes have steep sides with cones that stick out like huge bumps. They are built up when eruptions of viscous lava, tephra, and pyroclastic flows happen. It takes thousands of years for the pressure to build up enough in stratovolcanoes to cause an eruption. More than one kind of magma builds up in stratovolcanoes. They are basalt, andesite, dacite, and rhyolite magma. All of those magmas cause explosive eruptions except basalt magma. There are a lot of different vents around stratovolcanoes. Some of the vents are cinder cones and domes low on the sides of the volcano. Sometimes stratovolcanoes are called composite cones.


shield volcano

Shield volcanoes are large volcanoes that are built almost entirely of fluid lava flows. It has broad sloping sides and is usually surrounded by gently sloping hills in a circular or fan shaped pattern, that looks like a warrior's shield.
The volcano is produced by the action of the gas (steam or water vapor) with heat from the earth's core. This action melts rock turning it into magma. The pressure from the heat of the gas pushes the magma upwards till it explodes. Molten magma shoots upward from deep below the ocean floor and breaks through the drifting plates to form shield volcanoes. Lava flows gently and continuously out of the central volcanic vent or group of vents. This lava is very runny, and can't be piled up into steep mounds. It gradually accumulates and cools around the volcano. The eruptions are characterized by low explosivity lava-fountaining that forms cinder cones and spatter cones at the vent. The volcanoes are built up slowly by the accretion of thousands of highly fluid lava flows called basalt lava. The lava spread widely over great distances, then cools as thin gently dipping sheets. Lavas also erupt from vents along fractures (rift zones) that form on the flanks of the cone. Some of the largest volcanoes in the world are Shield volcanoes.

Batholith

Batholith

 If you come across an outcrop (exposure) of coarse-grained igneous rock, chances are you are standing on a pluton or batholith that crystallized several km below the Earth's surface. It may represent the magma chamber of an extinct volcano or a magma body that never produced any eruptions.

Batholiths indicate a long period of repeated igneous intrusions over a large area, such as might be expected along a subduction zone.

The Sierra Nevada Batholith

The Sierra Nevada Batholith of eastern California forms the largest mountain range in the continental U.S. Although the prospect of walking across huge areas of one type of rock--granite--might seem dull, in fact the Sierras offer spectacular scenery and lots of interesting details about what went on in the magma chambers of a suite of subduction zone volcanoes that were active from roughly 150 to 80 million years ago. Intrusive rocks offer many clues as to the inner workings of the Earth!

Gulf Currents

 The gulf stream
The Gulf Stream was first discovered in 1513 by the Spanish explorer Juan Ponce de Leon and was then used extensively by Spanish ships as they travelled from the Caribbean to Spain. In 1786, Benjamin Franklin mapped the current, further increasing its usage
Path of the gulf stream
Today, it is understood that the waters feeding into the Gulf Stream begin flowing off the west coast of Northern Africa.There, the Atlantic North Equatorial Current flows from that continent across the Atlantic Ocean. Once the current reaches eastern South America, it splits into two currents, one of which is the Antilles Current. These currents are then funneled through the islands of the Caribbean and through the Yucatan Channel between Mexico and Cuba

plate tectonics

The San Andreas fault is a crack in the Earth's crust in California, some 1100 kilometers long. Many earthquakes have occurred along it, including famous ones in 1857, 1906 and 1989. It is the boundary between the North American and Pacific lithospheric plates. Geologists divide it into several segments, each with distinct behavior. A research project has drilled a deep hole into the fault to study the rock there and listen for earthquake signals.

 

The San Andreas fault is the foremost of a large set of faults along the plate boundary between the Pacific plate on the west and the North American plate on the east. The west side moves north, causing earthquakes as it moves. Over millions of years, it has brought very different sets of rocks to face each other across the fault trace. The forces associated with the fault have pushed up mountains in some places and stretched apart large basins in others. The mountains include the Coast Ranges and the Transverse Ranges, both of which consist of many smaller ranges. The basins include the Coachella Valley, the Carrizo Plain, the San Francisco Bay, the Napa Valley and many others. The California geologic map will show you more about those.